The present invention is related in general to optical or electrical switches and more particularly to a method and apparatus for optical or electrical switching in response to a predetermined mechanical stress or load.
Many devices are activated in response to the application of a mechanical force. For example, some munitions systems are designed to activate (or deactivate) in response to an impact force or a percussion. A typical percussion fuze for a munition includes a mechanical inertial mass that strikes a fulminating compound in response to impact of the munition or a rapid deceleration. In another example, supplemental inflatable restraint systems (e.g., air bags) employ a variety of force sensors to activate the system. Typically, these sensors are mechanical/inertial units with a rotor, an eccentric mass and contacts. If deceleration is sufficient, the mass causes the rotor to turn, pushing the points together and activating the air bag. Some supplemental inflatable restraint systems include decelerometers, i.e., cantilevered tab-type strain gauges that bend under deceleration and close contacts to activate the air bag. In addition, some supplemental inflatable restraint systems include a mercury switch having contacts at the top of a tilted tube that is partially filled with mercury. When a rapid deceleration occurs inertia forces the mercury up into the tube to the contacts and bridges the gap to activate the system. Of course, reorienting the tube will also have the same effect.
The foregoing force activated switches in general depend upon a variety of mechanical elements such as levers, cantilevers, springs, dashpots, or the like, that can jam, become misaligned, leak, or otherwise fail due to their inherent design complexity. The present invention solves the foregoing problems, at least in part, by providing a method and apparatus that employs a composite material that fails at specific applied loads that can be tailored to the application.
The above-mentioned concerns are addressed by the present invention and will be understood by reading and studying the following specification.
According to a broad aspect of a preferred embodiment of the invention, a switch that is activated by a predetermined mechanical load includes a first layer of plastic material, a second layer of plastic material, a layer of elastomeric material having first and second surfaces, the first surface bonded to the first layer of plastic material by a layer of adhesive material, the second surface of the elastomeric material bonded to the second layer of plastic material by a layer of adhesive and a conductor disposed within one or more of the layers wherein the conductive path is broken when at least one of the adhesive bonds is displaced by the predetermined mechanical load. In one embodiment the conductor is a wire or optical fiber enclosed within the layers. In another embodiment the adhesive material and at least one of the layers is made conductive by the addition of one or more conductive materials. In another aspect of the present invention, the strength of the bonds may be determined by one or more of the following: preparation of the bonding surfaces, curing of the adhesive material or selection of the adhesive.